1. Field of the Invention
The present invention relates to a method of manufacturing of an expansion sleeve having longitudinal slots, a bore, and a substantially cylindrical outer surface.
2. Description of the Prior Art
Expansion dowels with an expansion sleeve of the type described above are anchored in constructional components formed of concrete, stone, masonry and the like, with the expansion sleeve being radially expanded by an expanding member. The radial expansion is decisive for obtaining target anchoring values. The radial expansion insures frictional and, in certain cases, formlocking anchoring of the expansion dowel in the constructional component. The frictional anchoring or connection depends on the size of the outer profile or surface of the sleeve that frictionally engages the inner surface or wall of the bore in which a dowel is anchored. That is the smaller is the engaging surface of the expansion sleeve the smaller is the anchoring value.
German Publication DE-43 44 382 discloses a method of manufacturing of an expansion sleeve which can be radially expanded. To provide for radial expansion, the expansion region of the expansion sleeve is provided with longitudinal slots, whereby tabs are formed between the slots. The expansion sleeve is radially expanded by introduction of an expansion member into the sleeve bore tapering inward toward the front end of the sleeve. Upon the introduction of the expansion member, the tabs are displaced radially outwardly. After the radial expansion took place, i.e., after the expansion dowel has been completely set, a screw, a threaded rod and the like can be secured to the sleeve which is provided for that purpose with load application means in form of a thread that is located at the end of the sleeve remote from the expansion region. For manufacturing the sleeve, first the longitudinal slots are formed, and then, the tabs are substantially radially compressed to reduce the size of the slots to a most possible extent to provide as large as possible outer surface of the sleeve available for engagement with a bore wall.
The above-described method permits to obtain an expansion dowel advantageous in use but expensive in manufacturing and, therefore, not economical.
Accordingly, an object of the present invention is to provide an economical method of manufacturing of an expansion sleeve that would make the sleeve non-expensive.
Another object of the present invention is to provide a method of manufacturing of a non-expensive expansion sleeve having a large outer surface for engagement with a bore wall.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a method including providing a blank having axially extending material weaknesses, and forming the longitudinal slots by tearing open the material weaknesses by substantially radially expanding same.
Because the material weaknesses, which form the longitudinal slots, are teared open, the slots have a negligible width so that the sleeve has the maximum possible outer surface available for engagement with a bore wall.
According to an advantageous embodiment of the present invention, the material weaknesses are provided in the wall of the expansion sleeve bore and are formed as sharp, V-shaped grooves. Due to the simple formation of the slots, the method is very economical. Further, the tearing open process permits to obtain slots with complementary opposite teared-open walls.
The tearing open in the region of the material weaknesses is accompanied by heat treatment of this region, which favorably influences the tearing-open process. The selection of a treatment temperature is effected taking into consideration the material of the expansion sleeve. When the sleeve is made of a thermoplastic material, the operational temperatures are below the glass transition temperature. Thus, the temperature, e.g., for tearing open a sleeve formed of a propylene, can be selected below xe2x88x9215xc2x0 C.
Advantageously, the tearing open is effected by introducing into the bore of the expansion sleeve of a tearing mandrel, an outer diameter of which is greater than an inner diameter of the bore, at least in the region provided with material weaknesses.
The outer surface of the expansion sleeve is advantageously formed by applying to the outer profile of the sleeve of an inwardly directed force. Thereby a substantially cylindrical outer profile is provided insuring the availability of a maximum possible outer surface for engagement with a bore wall. This insures obtaining of an optimal carrying capability of the expansion sleeve in a bore.
Advantageously, the expansion sleeve is formed of a plastic material to insure an economical production of the expansion sleeve. For use under certain condition, e.g., in fireproof locations, the sleeve is formed of metal.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.